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UBC Theses and Dissertations

Development of molecular markers and cloning of genes involved in the biosynthesis of monoterpenes in Lavandula Adal, Ayelign Mengesha


Several species of the genus Lavandula (lavenders) are important plants grown for their essential oils (EO), which find extensive applications in cosmetics, personal care products and alternative medicines. The EO of these plants is mainly constituted of monoterpenes, the C₁₀ class of terpenoids. In this study, we investigated three aspects of lavenders using advanced genomic resources derived from EO-producing tissues of these plants. Firstly, we developed diagnostic simple sequence repeat (SSR) markers from expressed sequence tag (EST) databases to delineate closely related species. Over 250 SSRs (≥ 18 bp) were developed from L. angustifolia and L. x intermedia ESTs. Thirty-one EST-SSRs were validated, 24 of which had a strong discrimination power in donor plant species, and a considerable transferability into related species. Secondly, we identified and functionally characterized cDNAs encoding geranyl pyrophosphate synthase (GPPS), which produces GPP, the linear precursor to all regular monoterpenes. Lavender GPPS is a heterodimeric protein composed of a small subunit (LiGPPS.SSU1), and a large subunit (LiGPPS.LSU). Recombinant LiGPPS.SSU1 interacts with LiGPPS.LSU, catalyzing the condensation of isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) to produce GPP. Recombinant LiGPPS.SSU1 also interacts with lavender and N. benthamiana geranylgeranyl pyrophosphate synthase (GGPPS; the enzyme responsible for synthesis of GGPP, the linear precursor to diterpenes), modifying its activity to form GPP. Transcript levels for LiGPPS.SSU1 and LiGPPS.LSU parallel total monoterpene concentration, with more transcripts present in flowers where most of lavender EO accumulates. Finally, we cloned and functionally characterized lavender cDNAs encoding two monoterpene synthase genes, 3-carene synthase (Li3CARS) and S-linalool synthase (LiS-LINS), in vitro. Recombinant Li3CARS and LiS-LINS proteins converted GPP into 3-carene and S-linalool, respectively. Li3CARS transcripts and the levels of 3-carene were up-regulated by methyl jasmonate, suggesting a potential defensive role for 3-carene. The transcripts for LiS-LINS were also highly expressed in flowers, where S-linalool accumulates.

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